Added sass variables to sass import scope

src/sass/variables.scss

@@ -0,0 +1,2 @@
+$color-grey-md: #999;
+

webpack.config.js

@@ -162,6 +162,7 @@ module.exports = {
             reducers: path.resolve(__dirname, 'src/reducers'),
             sagas: path.resolve(__dirname, 'src/sagas'),
             selectors: path.resolve(__dirname, 'src/selectors'),
+            variables: path.resolve(__dirname, 'src/sass/variables.scss'),
             sprite: path.resolve(__dirname, 'src/images/sprite/sprite.scss')
         }
     },